"According to the Court, ho wever, the police officer in this case, Detective Bartelt, committed a trespass because he was accompanied during his otherwise lawful visit to the front door of respondent’s house by his dog, Franky. Where is the authority evidencing such a rule? Dogs have been domesticated for about 12,000 years; they were ubiquitous in both this country and Britain at the time of the adoption of the Fourth Amendment; and their acute sense of smell has been used in law enforcement for centuries. Yet the Court has been unable to find a single case—from the United States or any other common-law nation—that supports the rule on which its decision is based. Thus, trespass law provides no support for the Court’s holding today."
IOW, using the dogs to sniff was the equivalent of a cop walking up to the window and doing the “peeping tom” thing.